Not all stereo images are necessarily realistic looking. All
manner of distortions and special effects can be introduced into a
stereo image, either deliberately or incidentally. Depth may be
exagerrated or compressed, and the apparent scale of the subject
may be enlarged or reduced. These effects are the result of
variables associated with the picture taking, and/or in
combination with the viewing method. When a view does reproduce
spatial realism faithfully, it is called an orthoscopic view.

For an "ortho" view, the angular field of view (as defined by
the focal length of the lens) of the camera must match the angular
field of vision of the observer (this could be defined by the
focal length of the viewer's optics). Furthermore, the two
viewpoints recorded by the camera must be separated by the same
distance as the distance between a typical observer's eyes: about
65mm. This distance is called the "stereobase" or "interaxial"
separation (also i/a separation).

On this website, viewing is done without the aid of optics, so
the field of view of the observer will be a function of image size
on screen and the distance from the observer's eye to the screen.
Because of the limitations of presentation on a video screen, not
all of the views on this site will appear orthoscopic. However, I
have prepared most of the enlarged close-ups and anaglyphs to
appear close to "ortho" on most computer monitors.

I shoot slides to be viewed in an inexpensive
viewer that has 50mm focal length optics. Such a viewer presents the
highest quality, affordable three dimensional image. Therefore, to
achieve maximum realism in this viewer, I only shoot with 50mm
lenses on my camera.

Depending on the type of subject, a stereo photographer may use
techniques that cause the resultant view to look necessarily
unrealistic, but nevertheless contain impressive
three-dimensionality.

Macrostereo

One such example is with macro stereography. Here the two
viewpoints that are recorded are brought closer together, to a
distance scale more in line with the size of the subject. There's
nothing quite like a stereo photograph of an ant. But to
photograph an ant for interesting stereo viewing requires that the
ant looks huge! It's not very realistic (there are no huge
ants...), but it is a valid and popular form of stereography. Look
at this nice example of a macro view of a couple of pennies, on
display courtesy of
Gabriel Jacob:

Hyperstereo

The opposite example is the so-called hyperstereo. It is an
appropriate technique for very large subjects, such as a city
skyline or aerial view. The two viewpoints recorded are relatively
far apart (up to dozens of feet), and this gives greater spatial
relief to the subject. Unfortunately it also causes the subject to
appear miniaturized. Below is an example of a hyper aerial view of
Boston, on display courtesy of Ron
Labbe.

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